Induction heating



April 1946. NB. STEVENS 2,337,629

INDUCTION HEATING Filed June 18, 1943 2 Sheets-Sheet '1 j v-Lsorv' 5.STEVE/V6.

ATTO/P/VEKS.

April 2, 1946.

N. B. STEVENS INDUCTION HEATING Filed June 18, 1943 2 Sheets-Sheet 2GUENCHING FLU/D v INVENTOR. I I ZVZISO/VfiJTfi/EMS.

Z M CM Patented'A r. 2, 1946 INDUCTION HEATING Nelson B. Stevens,Woodhaven, N. Y., assignor to Induction Heating Corp., New York, N. Y.,a corporation of New York Application June 1a. 194:, Serial No. 491,304

zclaims.

This invention relates to induction heating, and apparatus therefor,which is particularly'adapted among other possible uses, for internallyheating objects with small cavities.

The internal induction heating of objects such as engine cylinders andthe like has generally heretofore been accomplished by inserting a workcoil having a number of turns arranged coaxially with the cylinder orcavity. But such an arrangement would be difllcult and have seriousdisadvantages if applied to the problem 01 internally heating cavitiesof small diameter. The conductor turns of the work coil have to berelatively large in order to embody a cooling fluid conduit and also tobe able to conduct sufficient power for rapid heating eilects. Hence, ifthe cavity to be heated is small, there will be insufficient spaceavailable for convenient coaxial arrangement of the conductor turns, andin general it would be difllcult to conduct suilicient high frequencypower into the cavity for rapid, economical heatin According to thepresent invention, the above noted difilculties are avoided by using awork "0011 comprising preferably a single turn having the general shapeof a hairpin, adapted to be inserted longitudinally into the smallcavities form of apparatus assembly embodying the invention;

to be heated. Such a hairpin turn, when its ter- 1 minals are connectedto a source of high frequency powe'r, sets up a magnetic field, thelines oi force 01 which mostly extend in planes perpendicular to thelongitudinal center line of the turn, as contrasted with the priorpractice where the lines of force extend along planes which are ingdrawings which form a part of this specification and illustrate merelyby way of example, preferred forms oi the invention. The inventionconsists in such novel features, arrangements and combinations of parts,and methods as may be shown and described in connection with theapparatus herein disclosed.

In the drawings: I

Fig. 1 is a side elevational view of a preferred In Fig. 1 portions of ahigh frequency source of power are shown in the form of a transformerIll having a secondary II and forming a part of high frequency generatorequipment such for example as shown in patent to Dravneek No. 2,321,-

189. Secondary terminals for the transformer are shown at l2, l2. Theserespectively may be connected to lugs as at l3, 83', on which a pair ofconductor bars 54, 14 are supported, as shown in further detail in Fig.4. A cooling fluid conduit as at i5 of non-magnetic metal may be brazedto one or the lugs l3 and also along the bar it as at W. The outer endof bar i4 may be bent downwardly as at it, and formed as shown in Fig. 2with a somewhat angularly disposed drill hole ii, through which theconduit i5 extends. From the lower end of portion. 55, the conduit iscontinued in the form oi? a depending hairpin-shaped work coil isadapted.

to be inserted in the cavity is of an object 20,

which is to be heated internally.

The return end or terminal of the work coil 18 may pass up through adrill hole as at ll within a depending portion it on the conductor bar54, and thence back to the transformer to a fluid outlet, in asymmetrical arrangement with respect to the corresponding other half ofthe structure above described. Thus, the cooling fluid conduit l5, l5may be integrally formed as one single piece of metal tubing, togetherwith the work ooiY I8 and the return connection therefor.

The term work coil as herein used is intended to apply to substantiallythat part of the structure, such as at l8, which is to be in activecoupling relation with the work piece.

As shown in Figs. 2 and 5, the conductor bars i4, it may be separated bya strip of insulation as at 2|. Also these conductor bars may be seemedtogether to bolts pls w more heat to these portlozoe. this t de as atelmtole ptocluolne e eutetemtlelly uniform As shown, the transformerltlmay Zoe mounted heating effect tn the work piece tmoughout on e,roletiorm 23 forming of a cabinet etruo depth of the cavity ls, et theupper tm'e having at front meet formed tvltJo, 5 eml of the eevltv therewill be e. greater lose oi aperture 25, through wheels Work. eol1 heatby teelietlen. thus tequlzclng the supply J porting structure extends.be of more heat at this portion it 1103 to 3 m t located in front of35393161 265 to the same degree as the middle portion. Also epoamtus forelevating; H'lidlowering the work since lower portion of the cavitysmtoumel= o' 0 nd. out o1? ooeretle fooeltien em eel by a larger emouotof metal, more laeet fie re 1866 l. m w o Q n v 19 1 1 i for alsorotating the @Ulllli the tte fitment. qutretl to relse toe temperatureof true portton temple eomprlse 2, go to the degree as that ot themltlelle portion. l. views 28. within Hence the bowed. eide portions, asshown, pro lowe the upper vitle it simple expedient :Zor ecoomplishlngnext of homing e9 9. oclsm form o1? the'cevtty Wells throughout the t mthe in. Th o o2 lowezc he mt thereol. The desired. uniform at theplatform. :Yooezz eompree a 39 emu?) the 15g wbmve eX hydraulic @istozlol emteiole lmom lle-mod, eccomgolishecl by reletlve rotation of form esat St. t coil and. work piece, The oegtee to wktlclo. A ter .oe G9 taeportions oi the tame. must Zoe IGDWGIL, mtg; 2? and, eomeoted t3 v 2 toe, be zeetllly determined log; trlel, and. Wlll of eon: e vertical r emlwith depend upon. the elle'oe and proportions of tee ot teeelvlw wort:piece and its eevltz' A5 shown to. 2 end. 3, the work 2U the housing 28,so to the WQZE pieces piling ege peer .o oometm w is intended to have I.portions 2 3' to range as to lee its outer surface the induction heatingoz: the

member 2 htemelly. Elle is, Ems mey init ally held in place by anysuitable claw meant {not shown) and with. metal is extending alongtlaetoeee oz" each tin. l luotively the member I the eloove describedmetmer, the Tore will melt em"; creep beeeath lease 'ley eapill" erobjeot as r. onto r he wort; piece. or case only ts are to be ElmlQCh-Edongulerly *N to heat or vettical center pieces. Thus t positions. lltermay be coupled operated te eleve 4 e13 stationery post 1, 15; is e h eof Work shown in ggmp isi gg in conneotloo rotation t3.

he melee.

the invention shown in Z1 1.?

J is also the tut is (settled 10:; shaft so the {39 permit rotation asindicated, also vertlc movement fol .LZ'lBGIZiOIQ. and removal of thetwo piece as in the case of 1. After the piece has been heated to e,suficient temper eoneeewezo). ture for desired heat-treating, water o1other 1e elreult will lee less. quenching fluid be introduced. into thecowexample, w rk 31 alt-y as through e, nozzle 38' eosltloned with itso3". t. in-cif. with c centage each an air gap will be reluctance of itsl 'x/"lth the parttot";

Shown in g, fig w g m am 'g m tip in between the spread-apart terminalsof the some inwerc lv the longitudinal een hairpin ter line, whereby theportions totvetel lower While the examples of Figs. 2 and 6 both lateorhead end, and toward the upper o1 tem'llnel m volve internal heating ofsmall diameter surfaces ends, extend gradually outwardly irom the cen=of revolution, it will be understood that the same 'ter line, ascompared. with the intermediate porr sim ar appa tus may b us d in p ati e f r time of the tun. shape permits closer heating within cavitiesof non-ciroular cross seceoupling with the wort: piece at the app andtlon. Although. in that case the degree of tml= lowez: eml portions theoevlty for? mp 5 5 tomlltv of heating at cllfietent points about thecenter line of the cavity will not be quite so exact, yet since thecavities are small, the heat will be generally adequately distributed byconduction in the metal and also to some extent by the effects of eddycurrents.

Figs. 7-9 show a suitable form of work coil 40, also of the generalshape of a hairpin for heating the walls of a cavity as at 4| havingrestrictions as at 42, 43 at various elevations. In this case the workpiece 44 containing the cavity may be mounted on a vertically movablesupport 45, rotatable about the vertical axis of the cavity 4!. Theincoming conductor portion 46 (Figs. 8, 9) extends along and adjacentone element ofthe surface of revolution of the cavity, then reversing at41 for extension as at 48 along and adjacent another element of suchsurface, and thence out of the cavity.

The side portions of the hairpin configuration are both bent in the samedirections to laterally offset positions as at 49, 50 (Fig. 7), therebyproviding a shape to substantially correspond to the contour of elementsof the side walls of the cavity at portions of varying diameters.Because of these laterally offset portions, this form of work coil turncannot be arranged with its two side portions symmetrical with the axisof the cavity, and with close coupling relationship to the cavity walls,while still permitting insertion and removal of the work coil.Accordingly, here the vertical center line of the Work coil ispreferably arranged along but in spaced relation to the vertical axis ofthe cavity, as is best shown in Fig. 9. This still permits both sideportions of the hairpin configuration to extend along in close inductiverelation with elements of the surface of revolution being heated. Toinsert or remove the work piece in the apparatus without jamming theoffset portions 49, 50 against the walls of the cavity, it is firstnecessary of course to slide the work piece sideways to bring the workcoil to a more 'central' position to clear the restrictions 42, 43.

Hairpin-like coil turns such as of Fig. 7, are also adapted to heatstraight-walled cavitiesto different degrees at different elevations.For that purpose, offset portions as at 49, 50 would be located atelevations where less heating is desired.

With the above described examples of the invention, it has been foundpossible to quickly heat to redness the internal walls of objects suchas shown, upon making flow through the work coil turn, current at afrequency for example of 375,000 cycles. It is found that such objectshaving cavities for example of about /2 inch in diameter, and 1 /2inches in depth, could be thus heated by supplying to the work coilabout 5 kilowatts at such frequency, and with approximately 300 voltsacross the upper ends of the hairpin turn.

While the invention has been described in detail with respect to acertain preferred example, it will be understood by those skilled in theart after understanding the invention that various changes andmodifications may be made without departing from the spirit and scope ofthe invention, and it is intended therefore in the appended claims tocover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. A high frequency work coil for applying heat by magnetic inductioninside a cavity of an object, comprising a turn formed with a coolingfluid cavity therein and having the general shape of a hairpin, thesides of which are bowed I somewhat inwardly toward the longitudinalcenter line, whereby the portions toward the head end and toward theterminals extend gradually outwardly from said center line as comparedwith the intermediate portions of the turn.

2. Method for the induction heating of' the internal walls of smalldiameter cylindrical cavities, which comprises the steps of inserting ahollow conductor turn into the cavity in position to extend along andadjacent one element of the side wall of the cavity, then across andreturning along and adjacent another element of the side wall of thecavity and out thereof, the sides of said turn which extend along saidelements being so positioned as to be bowed somewhat inwardly toward thelongitudinal center line of the cavity, whereby the portions of the turntoward the outlet end of the cavity and toward the base of the cavityextend gradually outwardly from said center line as compared to v theintermediate portions of the turn, conducting a stream of cooling fluidthrough the hollow turn, and applying high frequency current to theturn, whereby heating of the cavity walls is caused by a magnetic fieldhaving its lines of force extending along planes generally perpendicularto the axis of the cavity.

NELSON B. STEVENS.

